The present invention relates to transmission systems and more particularly to voice operated transmit (VOX) control of audio information transmission.
There are known in the prior art a variety of voice-activated systems which initiate and terminate the transmission of audio information based upon the voice signal input to the microphone of a transmitter. In such systems, the input signal received by a microphone is usually compared in a threshold circuit designed to detect the presence of signals representing human speech. Thereafter, upon the detection of the presence of speech, a conventional radio transmitter, or similar transmission device, is activated to transmit the audio received by the microphone.
While such prior art systems have been in use for some time, the same are subject to various problems which limit their usefulness and versatility in various environments and prevent their efficient operation under a variety of circumstances. In particular, once the hardware has been configured to detect a certain feature of the voice signal, any reception of that signal by the transmitting microphone will cause keying of the transmission system to initiate audio transmission. Thus, if the environment in which the voice is to be transmitted contains noise or other sources of signals containing the same components detected by the voice detection circuitry, the voice operated system will key on that same signal. Because various environments contain background noise which may include signals similar to that on which the voice activation is determined, there is high probability that the system will be keyed during times when no voice is being provided to the microphone. In the same manner, unkeying of the system may be prevented following the termination of the audio transmission because of the presence of similar signals in the background or environment which are detected by the microphone and maintain the system in a keyed condition.
The consequences of the above operation result in systems which are slow to key and slow to unkey, thereby producing undesirable operating conditions. Thus, an audio transmission may be keyed when no voice is actually present at the transmitter, and may continue to be keyed following removal of the voice from the transmitter. Because of the limited adjustments that can be made in the hardware of conventionally employed detection circuitry, any attempt to narrow the response of the voice detection circuitry to limit unwanted keying usually produces a high rate of inaccuracy resulting in a failure to key on a voice signal or necessitates the use of the circuitry in only low noise environments. As a result, use of VOX systems is discouraged in favor of the more common manual keying systems of the prior art.
In an effort to improve efficiency and eliminate the required manual keying in a variety of audio systems, there is a continuing need for improved voice detection and control circuitry capable of enabling voice operated control. Accordingly, the present invention has been developed to overcome the specific shortcomings of the above known and similar techniques and to provide a voice operated transmit control system having improved reliability and versatility for voice activation.